The present invention relates to an aluminum alloy product having improved combinations of strength, toughness and corrosion resistance. This invention further relates to an aluminum-zinc-magnesium-copper alloy having at least about 10% greater yield strength than 7X50-T6 aluminum, the strongest aluminum alloy currently in wide use for demanding aerospace applications such as upper wing members, with toughness and corrosion properties comparable or superior to those of 7X50-T6 aluminum.
Precipitation-hardened 7075 alloy products exhibit high strength values in the T6 temper. Aluminum alloys, 7050 and 7150, exhibit still higher strengths in T6-type tempers. Should 7075 and 7X50 alloy products be artificially aged to a T76, T74 or T73-type temper, their resistances to stress corrosion cracking and/or exfoliation corrosion improve, in the order stated (with T73 being best), but often at some cost to strength vis-a-vis the T6 condition. The overall performance levels of 7X50 alloys greatly exceed those of 7075 aluminum, or other 7XXX alloys currently in wide aerospace use.
Another T7-type designation was recently registered for the aforementioned 7XXX alloys, that being T77 tempering which attains strength levels at or near strength levels associated with T6 temper in combination with T76, or even T74, corrosion resistance properties. Means for aging to this temper are set forth in U.S. Pat. No. 4,477,292 and British Patent No 1,480,351, the disclosures of which are fully incorporated by reference herein.